Phase modulation



P'atented Nov. 23, I937 PATENT OFFICE PHASE MODULATION Werner Buschbeck, Berlin, Germany, assignor to Telefunken Gesellschaft fiir Drahtlose Telegraphic in. b. H., Berlin, Germany, a corporation of Germany Application January 21, 1936, Serial No. 60,141 In Germany February 19, 1935 3 Claims.

This invention pertains to a circuit organization adapted to phase modulation of wave energy. An object of the present invention is to provide an arrangement adapted to insure pure phase 7 modulation in oscillations without the production where a is the cyclic frequency (angular velocity) of the alternating voltage.

. According to this invention, the arrangement of the German patent is to be modified in such a way that L and C change places; in other words,

= so that the resistance R is placed either in series with the capacity or in shunt to the inductance. If to is again the angular velocity of the oscillation to be modulated, then, in the case of the present invention, the relation 2 2 must be preserved.

The arrangement of the invention offers advantages in several regards which means a progress of the art. A certain difliculty inherent in the former arrangement was that the inductance ofL always presented some ohmic resistance which could not always be reduced to sufficiently low levels. In order to prevent undesirable and unfavorable efiects of the said ohmic resistance, recourse must be had to comparatively complicated circuit organizations. Now, this shortcoming is obviated in this invention. Another point that must be kept in mind is that, as can be followed from a comparison of the relations between angular velocity and the constants'of the oscillatory circuit, smaller elements for the latter may be used according to this invention, for the same wave frequency. Another advantage will be drawn attention to in connection with the discussion of an exemplified embodiment of my invention.

In describing my invention, reference will be made to the attached drawing wherein:

Fig. 1 is a simplified circuit diagram of my phase modulator:

Fig. 2 is a somewhat more complete diagram of my phase modulator connected with an amplifier:

Figs. 1a. and 2a are modifications of the arrangements of Figs. 1 and 2; while Fig. 3 is a graph illustrating the manner in which phase modulation is produced.

The following calculation is to show and prove that in a circuit arrangement of the kind here disclosed a variation of the resistance R merely insures a phase shift of the voltage arising across the condenser C whose absolute magnitude is preserved. A source of alternating voltage E, which is preferably free of resistance, works upon a circuit system comprising a capacity C and in series therewith a parallel arrangement of an inductance L and an ohmic resistance R (as shown in Fig. 1). Across the condenser C is to be made available a voltage Ec whose phase is made variable, While the value of the resistance R is to be varied at the rhythm of the modulating potentials. The voltage equations for the branch currents J l and J2 flowing through arbitrarily chosen paths indicated by the arrows are:

J1-1' XL XC -J2-7'XL=E -J1-7'XL+J2(R+7'XL) =0 where X1. and X0 are the reactances of inductance L and capacity C, respectively, E is the voltage of the alternating voltage source bearing the same reference letters, and

From these equations, the branch current J1 is found to be E L C'+j L C) If the condition here laid down, i. e.,

By evaluation of this equation, it is found that the phase position of vector E in relation to the ,In other words, it'is constant, and this'i's what was tobedemonstrated.

In the special case R= 0 there becomes For , iii] *1 v v The position of the vector Ec, as will. thus be seen, upon variation of-resistance .R from 0 to infinite,,is shifted by fully 180 degrees, from the inephase condition as far as phase opposition.

Derivations would be analogous in the case where the resistance R is in series with the condenser C. V The resistance R whose value is' to be changed at the rhythym'of themodulation process may consist of a'contact type microphone as shown in Fig. 2a, or of the discharge path of a tube whose internal resistance is controlled by the voice voltage applied between the cathode and the control electrode, .as shown in Fig. let, all in a Way familiar to the man trained in this art..

One particular merit of the arrangement here disclosed flows from its practical application under'normal working conditions. On the lefthand side in Fig. 2, is shown the scheme illustratedv in Fig. 1 in which the phase-modulated alternating voltage arises across the condenser C whence it is takenofi and applied to an amplifier stageV, a multi-stage transmitter are ordinarily accommodated in separate casings, and since the 1 master oscillator is usually mounted a certain distance apart with a viewtominimizing reaction ;of' the power stage upon the master oscillater, the transfer of the phase-modulated'alternating voltage from. the condenserC to the grid circuit of the! tube V is eifected byway .of an energy feed lead comprising an inner conductor iandan outer conductor a, for instance. (Secondary circuit elements "associated with the amplifier'stage V which are immaterial from the viewpoint of this invention, have been omitted for the sake of greater clearness of' illustration), It will be noted that the-said energy feeder terminates at both ends in a capacity;

Inasmuch as the various stages of i. e.-, at one end, there'is the condenser C, while at the other end there is the grid-cathode capacitance Cgk, so that such disturbing resonance actions are precluded as would'be produced, for

instance, if the voltage output occurred at an inductance. V I I Y r The fact that the modulation scheme here disclosedinsures very'favorable workingproperties a ,will become evident from the graphs in Fig. 3. V These show the dependence of power consumption and phase'angle upon the size of the resistance R. Along the abscissa. axis'is indicated'the'relationship between the non-reactive (effective); resistance Randi the 'reactance Xc.

Along the ordinatejaxis are'indicated, on the one hand, the-phase angle between the condenser alternating potential EC andthe M, FLofthe generator E, and, on theother hand, the relation .between non-reactive power N=J R and the condenser reactive power I 7 E2 X0 It will benoted. therefrom that the curvatureof the -curve is so slight that no special'means to correct distortion, under ,average requirements regarding transmission fidelity, will be necessary,

while in addition theload of the generator stays practically'stable insidealarge modulation range. Q30 1. In a circuit for producing phase modulae' What is claimed is:

tion ofalternating voltages, a source ofalternating voltages of constant frequency and amplitude, I an alternating current circuit including a capac ity and an inductance in series, and a resistance in parallel with said inductance, means'for varying said resistance at the rhythm-and rate. of modulation potentials, the inductance'and capac 1ty of the said alternating current circuit being so chosen that they will approximately obey the formula v LC r where w is the angular velocity of the'sup-plied alternating'voltage, and means for applying volt-j 1 ages frorn'said source to said circuit. A 2. A circuit arrangement accordingto'claim l,

ternal resistance of'a discharge tube. 3. In a phase modulation system, a source of oscillations, an inductance and a condenser in in which the variable resistance includes-the inseries with each other andwith said source, .a

resistance variable at signal frequency connected in parallel with said inductance,,an amplifier tube having a controlfelectrode and a cathode, a

tubular conductor connecting oneterniinal of said condenser to the cathode of said' tube, anda conductor within said tubular conductor connecting theother terminal of said condenser to the control electrode of said tube. V I

.WERN'ER BUSCHBECK. 

